Abstract

Magnetic data from the northeastern Indian Ocean reveal east-west trending magnetic lineations 28 through 34, an abandoned spreading center (ASC) and part of the Cretaceous Magnetic Quiet Zone (CMQZ), which are used to reconstruct past tectonic processes involved in the evolution of the ocean. Offsets in the magnetic lineations outline the existence of four N-S trending fracture zones: 80°E, Indira, 84.5°E, and 86°E. The 84.5°E Fracture Zone (FZ) acts as a boundary separating oceanic crust with different magnetic isochron patterns. The pairs of magnetic lineations 30 through 32n.2 between the 86°E FZ and the Ninetyeast Ridge reveal an ASC of about 65 Ma age, parallel to ≈0.5°S latitude. The structure of the ASC is well-identified in seismic reflection data as an undulating basement topographic rise covered by up to 2 km of Bengal Fan sediments. The spreading center might have initiated its activity along with other spreading centers of the Wharton Ridge and India-Antarctica Ridge, after the first major plate reorganization of the Indian Ocean (about 95±5 Ma), but ceased shortly after formation of anomaly 30 (about 65 Ma). Then it jumped southward between anomalies 32n.2 and 33. The jump captured the oceanic crust of anomalies 30 through 32n.2 that initially formed on the Antarctica plate, but were later transferred to the Indian plate. The spreading centers in the vicinity of the Ninetyeast Ridge jumped several times southward, to maintain a close proximity to the Kerguelen hotspot.